The invention relates generally to fuel supply systems for marine propulsion devices, and more particularly to fuel supply systems for stern drive units. The invention also relates to fuel filters for internal combustion engines and, more particularly, to fuel filters used with electric fuel pumps that supply fuel to internal combustion engines of marine installations.
It is known to mount a mechanical fuel pump on a stern drive engine block. Such a mechanical fuel pump can "lift" fuel from a remote fuel tank to the engine. It is also known to use a roller-vane-type electric fuel pump in connection with a stern drive. Such a fuel pump has been located on a stringer, in the bottom of the boat, with an upstream filter. Such a pump cannot lift fuel to the engine. This type of pump "pushes" fuel to the engine. Lifting fuel is important for stern drive units because a primer bulb is not available. A primer bulb cannot be used on a stern drive because it would not pass the "burn test" (described below).
U.S. Pat. No. 5,036,822 discloses a submersible electric pump mounted on the engine of an outboard motor. Electric fuel pumps have not been mounted on stern drive engines because of, among other things, the adverse effect of vibration and heat transfer.
Fuel filters used with electric fuel pumps are usually provided downstream of the fuel pump. See, for example, White U.S. Pat. No. 3,239,064, issued on Mar. 8, 1966. Also, filter elements of fuel filters used with electric fuel pumps are not always readily removable for replacement.
Conventional marine installations include an internal combustion engine, a starter for cranking the engine to start the engine, and a fuel system for supplying fuel to the engine. The fuel system includes a mechanical fuel pump that has an inlet and an outlet and that is driven by the internal combustion engine, a fuel filter that has an inlet and an outlet, a fuel line connecting the fuel pump inlet to a fuel supply, a fuel line connecting the fuel pump outlet to the fuel filter inlet, and a fuel line connecting the fuel filter outlet to the internal combustion engine. The flow rate of fuel supplied to the internal combustion engine by the mechanical fuel pump is a function of the speed of the internal combustion engine, and the flow rate of fuel pumped by the fuel pump when the engine is being cranked is relatively low. With a dry fuel system, starting of the engine is delayed until the mechanical fuel pump, pumping fuel at the relatively low flow rate while the engine is being cranked, can draw fuel from the fuel supply through one of the fuel lines and supply sufficient fuel to the internal combustion engine, via the fuel filter and the other fuel lines, for the engine to start.
Conventional circuitry for preventing an electric fuel pump from operating when the internal combustion engine is not running typically includes an oil pressure sensing switch. In such a circuit, the fuel pump will only be energized while the oil pressure sensing switch senses an oil pressure, in the engine, above a predetermined threshold. If the engine stalls, the oil pressure in the engine will fall below the predetermined threshold and the oil pressure sensing switch will disconnect the fuel pump from its source of electrical energy. When the engine is being started, oil pressure must rise above the predetermined threshold before the oil pressure sensing switch will connect the fuel pump to the source of electrical energy. Thus engine starting is delayed until oil pressure rises above the predetermined threshold.